This application is a new submission for our Microbial Pathogenesis and Genomics training program, which was previously supported by a T32 from 2006-2016. We are requesting support for five predoctoral trainees per year. The program, which is based at the University of Pennsylvania and Children's Hospital of Philadelphia and is located on a single contiguous campus, includes twelve laboratories directed by well- established principle investigators and three junior investigators, who are newly appointed assistant professors. Based on the success of the previously funded program, this T32 will enable us to continue to recruit some of the best and brightest trainees from a talented pool at Penn and from a vibrant biomedical environment that offers a large number of outstanding research opportunities for students. The organized training mission of this T32 has helped our efforts to collaborate and interact more effectively as a group; our trainers have several joint NIH grants, numerous joint publications, and a network of robust collaborations that involve our trainees. Our research in progress meetings and seminars within the microbiology program have helped spur the rapid growth of exciting, collaborative work in bacterial pathogenesis, microbial immunopathogenesis, and bacterial metagenomics, with institutional support for deep-sequencing facilities, bioinformatics, and a germ-free mouse core playing important roles in these efforts. These resources have been expanded to the new Penn-CHOP Microbiome Program, which will be a major focal point for new research and collaborations within our T32. The retention rate of our previously funded program was perfect; no trainee left the program prematurely over the 10 years of funding. In addition, all of our former trainees have continued to work in Microbiology or closely related fields involving infectious diseases. Five of our previous trainees have obtained tenure-track faculty positions ? all at major universities. The research opportunities provided by the trainers in this program coupled with strong institutional commitment and an extensive and well-organized training program will continue to provide excellent predoctoral training in microbial pathogenesis and genomics.